Optical alignment of oval graphene flakes.

Patterned graphene, as an atomically thin layer, supports localized surface plasmon polaritons at mid-infrared or far-infrared frequencies. This provides a pronounced optical force/torque in addition to large optical cross sections and will make it an ideal candidate for optical manipulation. Here, we study the optical force and torque exerted by a linearly polarized plane wave on circular and oval graphene flakes (single layers of graphene). While the torque vanishes for circular flakes, the finite torque allows rotating and orienting oval flakes relative to the electric field polarization. Depending on the wavelength, the alignment is either parallel or perpendicular to the electric field vector. In our contribution, we rely on a full-wave numerical simulation and also on an analytical model that treats the graphene flakes in a dipole approximation. The presented results reveal a good level of control on the spatial alignment of graphene flakes subjected to far-infrared illumination.

Phase-change material-based nanoantennas with tunable radiation patterns.

We suggest a novel switchable plasmonic dipole nanoantenna operating at mid-infrared frequencies that exploits phase-change materials. We show that the induced dipole moments of a nanoantenna, where a germanium antimony telluride (Ge3Sb2Te6 or GST for short) nanopatch acts as a spacer between two coupled metallic nanopatches, can be controlled in a disruptive sense. By switching GST between its crystalline and amorphous phases, the nanoantenna can exhibit either an electric or a balanced magneto-electric dipole-like radiation. While the former radiation pattern is omnidirectional, the latter is directive. Based on this property exciting switching devices can be perceived, such as a metasurface whose functionality can be switched between an absorber and a reflector. The switching between stable amorphous and crystalline phases occurs on timescales of nanoseconds and can be achieved by an electrical or optical pulse.

A generalized Kerker condition for highly directive nanoantennas.

A nanoantenna with balanced electric and magnetic dipole moments, known as the first Kerker condition, exhibits a directive radiation pattern with zero backscattering. In principle, a nanoantenna can provide even better directionality if higher order moments are properly balanced. Here, we study a generalized Kerker condition in the example of a nanoring nanoantenna supporting electric dipole and electric quadrupole moments. Nanoring antennas are well suited since both multipole moments can be almost independently tuned to meet the generalized Kerker condition.

Tunable graphene antennas for selective enhancement of THz-emission.

In this paper, we will introduce THz graphene antennas that strongly enhance the emission rate of quantum systems at specific frequencies. The tunability of these antennas can be used to selectively enhance individual spectral features. We will show as an example that any weak transition in the spectrum of coronene can become the dominant contribution. This selective and tunable enhancement establishes a new class of graphene-based THz devices, which will find applications in sensors, novel light sources, spectroscopy, and quantum communication devices.